The present invention concerns the use of acid-stable fluorescent indicators in sorption agents for chromatography.
Sorption materials for chromatography are available as finished preparations already applied in thin layers on inert carrier materials. They are also available in loose form for user preparation of the final separating materials. Such sorption materials in many cases contain fluorescent indicators which, when irradiated with UV radiation, enable recognition of the substances separated in the developed chromatogram. In comparison with direct coloring of the chromatogram using special reagents, this method has the advantage that the separated substances can be made visible without change or even destruction of their structure. Destruction-free detection is especially necessary in preparative chromatographic methods. Furthermore, in multiple development chromatography, it is also of great advantage.
Hitherto, the indicator generally employed for this purpose has been a zinc silicate activated with manganese. However, it possesses a serious disadvantage in that its fluorescence is more or less strongly or even fully extinguished when it is treated with an acid. The severity of this deleterious effect depends upon the strength and concentration of the acid. This is a considerable disadvantage since, in many cases, acids are employed in the development of chromatograms, or, often, the sorbent layers are conditioned in an acidic atmosphere or impregnated with acids before the chromatography.
Calcium tungstate is used in large amounts as a fluorescent material for X-ray intensifying foils. Moreover, cadmium tungstate has also been suggested for this purpose. See U.S. Pat. No. 4,115,312.
Although these substances have been known for several decades, and it is also known that they are capable of visible fluorescence, none of these substances has ever been used in sorbents for chromatography.